<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=\, initial-scale=1.0">
  <title>三列布局（浮动）</title>
  <style>
    .left {
      width: 300px;
      height: 700px;
      background: red;
      float: left;
    }

    .center {
      height: 700px;
      background: yellow;
      margin-left: 320px;
      margin-right: 320px;
    }

    .right {
      width: 300px;
      height: 700px;
      background: green;
      float: right;
    }
  </style>
</head>

<body>
  <div class="left"></div>
  <div class="right"></div>
  <div class="center"></div>
</body>

</html>